Method, apparatus, signals, and medium for managing power in a hybrid vehicle

ABSTRACT

A method and apparatus for managing power in a hybrid vehicle is disclosed. The vehicle includes an engine, an electric motor, and an energy storage element coupled to the motor. The method involves receiving a request to supply operating power to drive the vehicle and responding to the request by selecting an apportionment of operating power between the engine and the motor from among a plurality of apportionments having respective operating costs such that the selected apportionment is associated with a minimum operating cost, the operating cost including at least an engine fuel consumption cost and a storage element lifetime cost. The method further involves causing power to be supplied by at least one of the engine and the motor in accordance with the selected apportionment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims priority to U.S.Non-Provisional patent application Ser. No. 12/925,403 filed Oct. 19,2010, which is a continuation of U.S. Non-Provisional patent applicationSer. No. 11/515,175, now U.S. Pat. No. 7,826,939, filed Sep. 1, 2006,the disclosures of which are hereby incorporated by reference in theirentirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to hybrid vehicles and moreparticularly to managing power in a hybrid vehicle having an engine, anelectric motor, and an energy storage element coupled to the motor.

2. Description of Related Art

Hybrid electric vehicles having an engine (such as an internalcombustion engine) and an electric motor, for providing power to thevehicle have become a viable alternative to conventional internalcombustion engine vehicles. While such vehicles may require more complexpower transmission components, this complexity is offset by improvedfuel consumption and a corresponding reduction in emissions ofpollutants from the engine.

Given the present climate of higher prices for fossil fuels, there is acorresponding desire to further reduce fuel consumption costs whenoperating hybrid vehicles. Hybrid electrical vehicles reduce fuelconsumption by apportioning the power required to operate the vehiclebetween the engine and electric motor, to cause these components tooperate at efficient operating points. For example, when moving slowlyor when starting off from a stationary position, the electric motor maybe considerably more efficient than the engine and in this case most ofthe power may be supplied by the motor. At higher speeds, where engineefficiency is better, a greater proportion of power may be supplied bythe engine. Accordingly, the management of power distribution betweenthe engine and the motor for a hybrid electric vehicle is an importantfactor in achieving the best overall efficiency, low fuel consumption,and minimizing operating costs.

There remains a need for improved methods and apparatus for managingpower in a hybrid vehicle.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided amethod for managing power in a hybrid vehicle, the vehicle including anengine, an electric motor, and an energy storage element coupled to themotor. The method involves receiving a request to supply operating powerto drive the vehicle and responding to the request by selecting anapportionment of operating power between the engine and the motor fromamong a plurality of apportionments having respective operating costssuch that the selected apportionment is associated with a minimumoperating cost, the operating cost including at least an engine fuelconsumption cost and a storage element lifetime cost. The method furtherinvolves causing power to be supplied by at least one of the engine andthe motor in accordance with the selected apportionment.

The method may involve assigning a relative weighting between the enginefuel consumption cost and the storage element lifetime cost, therelative weighting assigned in accordance with fuel prices and storageelement replacement prices.

The method may involve producing operating costs for each of theplurality of apportionments.

The motor may be operably configured to receive mechanical power and togenerate electrical energy for charging the storage element, themechanical power being produced while reducing or maintaining a speed ofthe vehicle, and the method may involve reducing the operating costs inproportion to a quantity of the electrical energy generated whilereducing or maintaining the speed of the vehicle.

Causing power to be supplied may involve producing an engine powercontrol signal and a motor power control signal in response to at leastone of a drive signal representing an operator requested power receivedfrom an operator input device and a current vehicle operating condition,the power control signals being operable to cause a least one of theengine and the motor to supply power in accordance with the selectedapportionment.

Producing the power control signals may involve producing power requestsignals in response to at least one of a current speed of the vehicle,and a current acceleration of the vehicle.

Producing the operating costs for the plurality of apportionments of therequested operating power may involve producing cost values for each ofthe engine fuel consumption cost and the storage element lifetime costand combining the cost values to produce an overall operating cost foreach of the apportionments.

Combining the operating cost values may involve producing a sum of theoperating cost values.

The method may involve storing information representing the plurality ofengine fuel consumption costs in a computer memory and producing theoperating costs may involve locating an engine fuel consumption costcorresponding to each of the plurality of apportionments of therequested operating power in the memory.

Locating may involve locating an engine fuel consumption costcorresponding to an engine torque and engine speed that satisfies eachof the apportionments of the requested operating power.

The method may involve producing a signal representing an operatingtemperature of the engine and locating may involve locating an enginefuel consumption cost corresponding to the operating temperature.

The method may involve producing a signal representing an actual fuelconsumption of the engine while operating the vehicle and updating thefuel consumption information stored in the memory in accordance with theactual fuel consumption of the engine.

Producing the operating costs may involve producing a fuel consumptioncost for each of the plurality of apportionments, the fuel consumptioncost including a fuel consumption cost associated with operating theengine to supply the apportionment of power, and a fuel consumption costassociated with operating the engine to replace energy supplied by thestorage element to operate the motor to supply the apportionment ofpower.

Producing the fuel consumption cost to replace energy supplied by thestorage element may involve producing a prediction of a quantity ofelectrical energy required to replace the energy supplied by the storageelement.

The method may involve storing information representing a plurality ofengine fuel consumption costs in a computer memory and producing thefuel consumption cost to replace energy supplied by the storage elementmay involve locating, in the memory, an engine fuel consumption costcorresponding to a minimum engine fuel consumption for replacing thequantity of electrical energy supplied to the motor by the storageelement.

Producing the prediction of the quantity of electrical energy mayinvolve predicting a quantity of electrical energy associated with atleast one of a discharge energy loss in the storage element whensupplying the quantity of electrical energy to the motor, a motor energyloss when supplying the apportionment of the requested operating powerto the vehicle, and a charging energy loss of the storage element whenreplacing the quantity of electrical energy in the storage element.

The storage element may have a desired state of charge and producing theoperating costs may involve producing a storage element lifetime costproportional to an expected deviation from the desired state of chargeassociated with operating at each of the plurality of apportionments ofthe requested operating power.

The method may involve producing a state of charge signal representing astate of charge of the storage element, the lifetime cost for eachapportionment being proportional to an absolute value of a differencebetween the apportionment and a quantity of power required to return thestate of charge of the storage element to the desired state of charge.

Producing the operating costs for the plurality of apportionments ofpower may involve producing operating costs for apportionments that meetat least one constraint criteria associated with an engine maximum powercapability, an engine maximum torque capability, a motor maximum powercapability, a motor maximum torque capability, a motor maximum brakingpower capability, a motor maximum braking torque capability, a storageelement maximum discharge power, and a storage element maximum chargingpower.

Selecting the apportionment may involve selecting an apportionmenthaving a minimum operating cost using a golden section search technique.

In accordance with another aspect of the invention there is provided anapparatus for managing power in a hybrid vehicle, the vehicle includingan engine, an electric motor, and an energy storage element coupled tothe motor. The apparatus includes a processor circuit operablyconfigured to receive a request to supply operating power to drive thevehicle. The processor circuit is operably configured to respond to therequest by selecting an apportionment of operating power between theengine and the motor from among a plurality of apportionments havingrespective operating costs such that the selected apportionment isassociated with a minimum operating cost, the operating cost includingat least an engine fuel consumption cost and a storage element lifetimecost. The processor circuit is operably configured to cause power to besupplied by at least one of the engine and the motor in accordance withthe selected apportionment.

The processor circuit may be operably configured to assign a relativeweighting between the engine fuel consumption cost and the storageelement lifetime cost, the relative weighting assigned in accordancewith fuel prices and storage element replacement prices.

The processor circuit may be operably configured to produce operatingcosts for each of the plurality of apportionments.

The motor may be operably configured to receive mechanical power and togenerate electrical energy for charging the storage element, themechanical power being produced while reducing or maintaining a speed ofthe vehicle and the processor circuit may be operably configured toreduce the operating costs in proportion to a quantity of the electricalenergy generated while reducing or maintaining the speed of the vehicle.

The processor circuit may be operably configured to produce an enginepower control signal and a motor power control signal in response to therequest, the request including at least one of a drive signalrepresenting an operator requested power received from an operator inputdevice and a current vehicle operating condition, the power controlsignals being operable to cause at least one of the engine and the motorto supply power in accordance with the selected apportionment.

The current vehicle operating condition may include at least one of acurrent speed of the vehicle, and a current acceleration of the vehicle.

The processor circuit may be operably configured to produce cost valuesfor each of the engine fuel consumption cost and the storage elementlifetime cost and to combine the cost values to produce an overalloperating cost for each of the apportionments.

The processor circuit may be operably configured to combine theoperating cost values by producing a sum of the operating cost values.

The processor circuit may include a memory operably configured to storeinformation representing the plurality of engine fuel consumption coststherein and the processor circuit may be operably configured to locatean engine fuel consumption cost corresponding to each of the pluralityof apportionments of the requested operating power in the memory.

The processor circuit may be operably configured to locate an enginefuel consumption cost corresponding to an engine torque and engine speedthat satisfies each of the apportionments of the requested operatingpower.

The apparatus may include a temperature sensor located on the engine andoperable to produce a signal representing an operating temperature ofthe engine and the processor circuit may be operably configured tolocate an engine fuel consumption cost corresponding to the operatingtemperature from the plurality of engine fuel consumption costs.

The apparatus may include a fuel consumption sensor operable to producea signal representing an actual fuel consumption of the engine whileoperating the vehicle and the processor circuit may be operablyconfigured to update the fuel consumption information in accordance withthe actual fuel consumption of the engine.

The fuel consumption cost may include a fuel consumption cost associatedwith operating the engine to supply the apportionment of power, and afuel consumption cost associated with operating the engine to replaceenergy supplied by the storage element to operate the motor to supplythe apportionment of power.

The processor circuit may be operably configured to produce a predictionof a quantity of electrical energy required to replace energy suppliedby the storage element to operate the motor for each of the plurality ofapportionments.

The processor circuit may include a memory operably configured to storeinformation representing a plurality of engine fuel consumption costsand the processor circuit may be operably configured to locate, in thememory, an engine fuel consumption cost corresponding to a minimumengine fuel consumption for replacing the quantity of electrical energysupplied to the motor by the storage element.

The prediction of the quantity of electrical energy may include aprediction of a quantity of electrical energy associated with at leastone of a discharge energy loss in the storage element when supplying thequantity of electrical energy to the motor, a motor energy loss whensupplying the apportionment of the requested operating power to thevehicle, and a charging energy loss of the storage element whenreplacing the quantity of electrical energy in the storage element.

The storage element may have a desired state of charge and the processorcircuit may be operably configured to produce a storage element lifetimecost proportional to an expected deviation from the desired state ofcharge associated with operating at each of the plurality ofapportionments of the requested operating power.

The storage element may be operably configured to produce a state ofcharge signal representing a state of charge of the storage element andthe processor circuit may be operably configured to receive the state ofcharge signal and to produce the lifetime cost in response to the stateof charge signal, the lifetime cost being proportional to an absolutevalue of a difference between the apportionment and a quantity of powerrequired to return the state of charge of the storage element to thedesired state of charge.

The processor circuit may be operably configured to produce operatingcosts for apportionments that meet at least one constraint criteriaassociated with an engine maximum power capability, an engine maximumtorque capability, a motor maximum power capability, a motor maximumtorque capability, a motor maximum braking power capability, a motormaximum braking torque capability, a storage element maximum dischargepower, and a storage element maximum charging power.

The processor circuit may be operably configured to select anapportionment having a minimum operating cost using a golden sectionsearch technique.

In accordance with another aspect of the invention there is provided acomputer readable medium encoded with codes for directing a processorcircuit to carry out a method for managing power in a hybrid vehicle,the vehicle including an engine, an electric motor, and an energystorage element coupled to the motor. The method involves receiving arequest to supply operating power to drive the vehicle and responding tothe request by selecting an apportionment of operating power between theengine and the motor from among a plurality of apportionments havingrespective operating costs such that the selected apportionment isassociated with a minimum operating cost, the operating cost includingat least an engine fuel consumption cost and a storage element lifetimecost. The method further involves causing power to be supplied by atleast one of the engine and the motor in accordance with the selectedapportionment.

In accordance with another aspect of the invention there is provided acomputer readable signal encoded with codes for directing a processorcircuit to carry out a method for managing power in a hybrid vehicle,the vehicle including an engine, an electric motor, and an energystorage element coupled to the motor. The method involves receiving arequest to supply operating power to drive the vehicle and responding tothe request selecting an apportionment of operating power between theengine and the motor from among a plurality of apportionments havingrespective operating costs such that the selected apportionment isassociated with a minimum operating cost, the operating cost includingat least an engine fuel consumption cost and a storage element lifetimecost. The method further involves causing power to be supplied by atleast one of the engine and the motor in accordance with the selectedapportionment.

In accordance with one aspect of the invention there is provided anapparatus for managing power in a hybrid vehicle, the vehicle includingan engine, an electric motor, and an energy storage element coupled tothe motor. The apparatus includes provisions for receiving a request tosupply operating power to drive the vehicle and provisions forresponding to the request by selecting an apportionment of operatingpower between the engine and the motor from among a plurality ofapportionments having respective operating costs such that the selectedapportionment is associated with a minimum operating cost, the operatingcost including at least an engine fuel consumption cost and a storageelement lifetime cost. The apparatus also includes provisions forcausing power to be supplied by at least one of the engine and the motorin accordance with the selected apportionment.

The apparatus may include provisions for assigning a relative weightingbetween the engine fuel consumption cost and the storage elementlifetime cost, the relative weighting assigned in accordance with fuelprices and storage element replacement prices.

The apparatus may include provisions for producing operating costs foreach of the plurality of apportionments.

The motor may be operably configured to receive mechanical power and togenerate electrical energy for charging the storage element, themechanical power being produced while reducing or maintaining a speed ofthe vehicle and the apparatus may further include provisions forreducing the operating costs in proportion to a quantity of theelectrical energy generated while reducing or maintaining the speed ofthe vehicle.

The provisions for causing power to be supplied may include provisionsfor producing an engine power control signal and a motor power controlsignal in response to at least one of a drive signal representing anoperator requested power received from an operator input device and acurrent vehicle operating condition, the power control signals beingoperable to cause a least one of the engine and the motor to supplypower in accordance with the selected apportionment.

The provisions for producing the power control signals may includeprovisions for producing power request signals in response to at leastone of a current speed of the vehicle, and a current acceleration of thevehicle.

The provisions for producing the operating costs for the plurality ofapportionments of the requested operating power may include provisionsfor producing cost values for each of the engine fuel consumption costand the storage element lifetime cost and provisions for combining thecost values to produce an overall operating cost for each of theapportionments.

The provisions for combining the operating cost values may includeprovisions for producing a sum of the operating cost values.

The apparatus may include provisions for storing informationrepresenting the plurality of engine fuel consumption costs and theprovisions for producing the operating costs may include provisions forlocating an engine fuel consumption cost corresponding to each of theplurality of apportionments of the requested operating power.

The provisions for locating may include provisions for locating anengine fuel consumption cost corresponding to an engine torque andengine speed that satisfies each of the apportionments of the requestedoperating power.

The apparatus may include provisions for producing a signal representingan operating temperature of the engine and the provisions for locatingmay include provisions for locating an engine fuel consumption costcorresponding to the operating temperature.

The apparatus may include provisions for producing a signal representingan actual fuel consumption of the engine while operating the vehicle andprovisions for updating the stored fuel consumption information inaccordance with the actual fuel consumption of the engine.

The provisions for producing the operating costs may include provisionsfor producing a fuel consumption cost for each of the plurality ofapportionments, the fuel consumption cost including a fuel consumptioncost associated with operating the engine to supply the apportionment ofpower, and a fuel consumption cost associated with operating the engineto replace energy supplied by the storage element to operate the motorto supply the apportionment of power.

The provisions for producing the fuel consumption cost to replace energysupplied by the storage element may include provisions for producing aprediction of a quantity of electrical energy required to replace theenergy supplied by the storage element.

The apparatus may include provisions for storing informationrepresenting a plurality of engine fuel consumption costs and theprovisions for producing the fuel consumption cost to replace energysupplied by the storage element may include provisions for locating, inthe provisions for storing information, an engine fuel consumption costcorresponding to a minimum engine fuel consumption for replacing thequantity of electrical energy supplied to the motor by the storageelement.

The provisions for producing the prediction of the quantity ofelectrical energy may include provisions for predicting a quantity ofelectrical energy associated with at least one of a discharge energyloss in the storage element when supplying the quantity of electricalenergy to the motor, a motor energy loss when supplying theapportionment of the requested operating power to the vehicle, and acharging energy loss of the storage element when replacing the quantityof electrical energy in the storage element.

The storage element may have a desired state of charge and theprovisions for producing the operating costs may include provisions forproducing a storage element lifetime cost proportional to an expecteddeviation from the desired state of charge associated with operating ateach of the plurality of apportionments of the requested operatingpower.

The apparatus may include provisions for producing a state of chargesignal representing a state of charge of the storage element, thelifetime cost for each apportionment being proportional to an absolutevalue of a difference between the apportionment and a quantity of powerrequired to return the state of charge of the storage element to thedesired state of charge.

The provisions for producing the operating costs for the plurality ofapportionments of power may include provisions for producing operatingcosts for apportionments that meet at least one constraint criteriaassociated with an engine maximum power capability, an engine maximumtorque capability, a motor maximum power capability, a motor maximumtorque capability, a motor maximum braking power capability, a motormaximum braking torque capability, a storage element maximum dischargepower, and a storage element maximum charging power.

The provisions for selecting the apportionment may include provisionsfor selecting an apportionment having a minimum operating cost using agolden section search technique.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

FIG. 1 is a schematic view of a hybrid vehicle in accordance with afirst embodiment of the invention;

FIG. 2 is a schematic view of a hybrid vehicle in accordance with asecond embodiment of the invention;

FIG. 3 is a schematic view of a processor circuit for use in the hybridvehicle shown in FIG. 2;

FIG. 4 is a graphical depiction of a fuel consumption map for an engineused in the hybrid vehicle shown in FIG. 2;

FIG. 5 is a graphical depiction of a storage element lifetime as afunction of state of charge, for a storage element used in the hybridvehicle shown in FIG. 2;

FIG. 6 is a flowchart of a process for producing operating costsexecuted by the processor circuit shown in FIG. 3;

FIG. 7 is a graphical depiction of operating costs for the hybridvehicle shown in FIG. 2; and

FIG. 8 is a schematic view of a hybrid vehicle in accordance with analternate embodiment of the invention.

DETAILED DESCRIPTION

Referring to FIG. 1, an apparatus for managing power in a hybrid vehicle11 is shown generally at 10. The hybrid vehicle 11 includes an engine12, an electric motor-generator 14, and an energy storage element 16coupled to the motor. The apparatus 10 includes a processor circuit 18,which is operably configured to receive a request signal 20 to supplyoperating power to drive the vehicle 11. The processor circuit 18 isoperably configured to respond to the request by selecting anapportionment of operating power between the engine 12 and themotor-generator 14 from among a plurality of apportionments havingrespective operating costs such that the selected apportionment isassociated with a minimum operating cost. The operating cost includes atleast an engine fuel consumption cost and a storage element lifetimecost. The processor circuit 18 is operably configured to cause power tobe supplied by at least one of the engine 12 and the motor-generator 14in accordance with the selected apportionment.

In the hybrid vehicle 11 shown in FIG. 1, the vehicle includes atransmission 22 and a pair of drive wheels 24. The engine 12 is coupledto the transmission 22 through a first shaft 26, and the motor-generator14 is coupled to the transmission via a second shaft 28. The first andsecond shafts 26 and 28 couple power from the engine 12 and themotor-generator 14 respectively, through the transmission 22, to thedrive wheels 24, thus supplying operating power to drive the vehicle 11.In general operating power may be supplied by either the engine 12, orthe motor-generator 14, or by the engine and the motor in combination.

The hybrid vehicle 11 also includes a fuel reservoir 30, which is incommunication with the engine 12 for supplying fuel to operate theengine 12. The engine 12 further includes an interface 32 which is incommunication with the processor circuit 18 for receiving an enginepower control signal from the processor circuit 18 to control an amountof power coupled to the transmission 22 through the first shaft 26.

The storage element 16 is in communication with the motor-generator 14for supplying electrical energy to the motor. The motor-generator 14further includes an interface 34 for receiving a motor power controlsignal from the processor circuit 18 to control an amount of mechanicalpower supplied by the motor-generator 14 to the second shaft 28 and tocontrol an amount of electrical power generated by the motor-generatorin response to mechanical energy provided by the second shaft.

The motor-generator 14 thus has a motor mode in which it converts energyfrom the storage element 16 into mechanical energy at the second shaft28 and a generator mode in which it receives mechanical power from thesecond shaft and converts it into electrical energy for storage in thestorage element 16. Alternatively, in other embodiments (not shown) thevehicle 11 may include a separate generator for charging the storageelement 16, in which case the motor-generator 14 would operate only inthe motor-mode.

The mechanical power provided by the second shaft 28 may be generated bythe drive wheels 24 while maintaining or reducing a speed of the vehicle11, and coupled through the transmission 22 to the second shaft 28.Alternatively, the mechanical power may be generated by the engine 12,coupled through the first shaft 26 to the transmission 22, which may beconfigured to couple the power to the second shaft 28.

Referring to FIG. 2, an alternative embodiment of a hybrid vehicle isshown generally at 50. The hybrid vehicle 50 includes an engine 52, anelectric motor-generator 54, a transmission 56, and a clutch 64. Theclutch 64 includes a first friction disk 66 and a second friction disk63. The clutch 64 is engaged by causing the friction disks 66 and 63 tobe brought into contact with each other and the clutch is disengaged bycausing the friction disks to be separated.

The hybrid vehicle 50 includes a first shaft 58 for coupling themotor-generator 54 to the transmission 56, and a second shaft 60 forcoupling the motor to the first friction disk 66 of the clutch 64. Thesecond shaft 60 and the first shaft 58 are coupled to opposite ends of arotor (not shown) in the motor-generator 54 such that power may becoupled between the first and second shafts 60 and 58, through themotor-generator 54. The hybrid vehicle 50 also includes a third shaft 62for coupling the engine 52 to the second friction disk 63 of the clutch64. The clutch 64 operates to cause the engine 52 to be selectivelyengaged or disengaged from the second shaft 60. In some embodiments (notshown) the motor-generator 54 may be located between the transmission 56and the drive wheels 24, and the motor may be coupled to supply andreceive power directly to or from the drive wheels.

The motor-generator 54 is in communication with the storage element 16for receiving electrical energy therefrom. The storage element 16 maycomprise a plurality of cells 17, and may further include circuitry (notshown) for generating a state of charge (SOC) signal indicating acurrent SOC of the storage element. In one embodiment, the cells 17 inthe storage element may include electrochemical cells 17, such as nickelmetal hydride (NiMH) storage cells. In other embodiments, the storageelement 16 may include a combination of electrochemical cells and/or astorage capacitor element, such as ultra-capacitor, for example.

In the embodiment shown the motor-generator 54 comprises a wound fielddirect current (DC) motor in which a magnetic field is provided byenergizing field coils (not shown). The field coils may be energizedusing electrical energy supplied from the storage element 16. In otherembodiments the motor may include a permanent magnet DC motor, or analternating current motor (AC). In general the motor-generator 54 isoperable to couple mechanical power to the first shaft 58 when receivingelectrical energy from the storage element 16, and is operable as agenerator when mechanical power is coupled to the motor through thefirst shaft 58 for generating electrical energy for charging the storageelement 16.

The hybrid vehicle 50 optionally includes a power converter 55 forconverting the electrical energy received from the storage element intoa form suitable for operating the motor-generator 54. For example, thepower converter 55 may include an inverter for converting direct current(DC) from the storage element 16 into alternating current (AC) foroperating an AC motor. Alternatively the power converter 55 may be aDC-DC converter for converting the DC current from a first voltage levelassociated with the storage element 16, to a second voltage levelsuitable for operating the motor.

In this embodiment, the hybrid vehicle 50 further includes an operatorinput device 70 for producing a drive signal representing an operatorrequested power. The operator input device may include a foot actuatedactuator, for example. The hybrid vehicle 50 also includes a speedsensor 72 which is in communication with the drive wheels 24 forproducing a speed signal representing a speed of the drive wheels 24.

An embodiment of a processor circuit for managing power in the hybridvehicle 50 is shown at 80 in FIG. 3. Referring to FIG. 3, the processorcircuit 80 includes a central processing unit (CPU) 120, a programmemory a parameter memory 124, a media reader 126, and an input/outputport (I/O) 128. The program memory 122, the parameter memory 124, themedia reader 126 and the I/O 128, are all in communication with the CPU120.

The I/O 128 includes an input 82 for receiving a request signal, aninput 84 for receiving a speed signal, an input 90 for receivingtemperature signals, an input 94 for receiving a fuel consumptionsignal, and an input 86 for receiving the SOC signal form the storageelement 16. The I/O 128 also includes the output 96 for producing anengine power control signal, an output 98 for producing a motor powercontrol signal, and an output 104 for producing a clutch control signal.

The media reader 126 facilitates loading program codes into the programmemory 122 from a computer readable medium 130, such as a CD-ROM disc132, or a computer readable signal 134, such as may be received from anetwork such as a telephone network or the Internet, for example.

The parameter memory 124 includes a store 136 for storing datarepresenting an engine fuel consumption map, a store 138 for storingdata representing a set of operating conditions of the hybrid vehicle50, a store 140 for storing data representing constraint limits for thevehicle, and a store 142 for storing control loop parameters.

The input 82 of the processor circuit is in communication with theoperator input device 70 for receiving the drive signal, the input 84 isin communication with the speed sensor 72 for receiving the speedsignal, and the input 86 is in communication with the storage element 16for receiving the SOC signal.

Referring back to FIG. 2, in this embodiment, the engine 52 alsoincludes a temperature sensor 88 for sensing an operating temperature ofthe engine, the motor-generator 54 includes a temperature sensor 57 forsensing an operating temperature of the motor, and the power converter55 includes a temperature sensor 59 for sensing an operating temperatureof the power converter. The input 90 of the processor circuit 80 is incommunication with the temperature sensors 88, 57, and 59 for receivingthe respective temperature signals.

The engine 52 further includes a fuel consumption sensor 92 forgenerating a signal representing an actual fuel consumption of theengine. The input 94 of the processor circuit 80 is in communicationwith the fuel consumption sensor 92 for receiving the fuel consumptionsignal. Fuel is supplied to the engine 52 from the fuel reservoir 30.

The engine 52 also includes an interface 100 in communication with theoutput 96 of the processor circuit 80 for receiving the engine powercontrol signal to control an amount of power coupled to the third shaft62.

The motor-generator 54 includes an interface 102 in communication withthe output 98 of the processor circuit for receiving the motor powercontrol signal for controlling an amount of mechanical power supplied bythe motor-generator 54 to the first shaft 58 and to control an amount ofelectrical power generated by the motor-generator in response tomechanical energy provided by the first shaft.

The clutch 64 is in communication with the output 104 of the processorcircuit 80 for receiving the clutch control signal. The clutch controlsignal has states representing engagement and disengagement of thefriction disks 63 and 66.

Operation

In the embodiment shown in FIG. 2, operating power is supplied to thedrive wheels 24 of the hybrid vehicle 50 through the transmission 56.When the clutch control signal is in the disengaged state, the engine isdecoupled from the second shaft 60 (and thus the first shaft 58), andthe motor-generator 54 supplies operating power to the vehicle. Themotor-generator 54 receives electrical energy from the storage element16 and produces operating power for the vehicle 50 in response to themotor power control signal received at the interface 102 from the output98 the processor circuit 80.

When the clutch control signal is in the engaged state, the engine 52produces a first portion of the operating power in response to theengine power control signal received at the interface 100 from theprocessor circuit 80, while the motor-generator 54 produces a secondportion of the operating power in response to the motor power controlsignal received at the interface 102 from the processor circuit 80.

When the motor power control signal causes the motor-generator 54 tocease producing power, operating power may be supplied by the engine 52,in which case no electrical energy is supplied to the motor (or to themotor field coils) from the storage element 16 and the motor rotatesfreely, consuming only a small amount of energy due to residualmagnetism and windage effects (i.e. when the motor is not operating as agenerator).

When it is desired to charge the storage element 16, power is coupled tothe motor-generator 54 through the first shaft 58. The power is suppliedeither by the engine 52 or by the drive wheels 24. The drive wheels 24provide power to the first shaft 58 while reducing or maintaining thespeed of the vehicle 50. For example, when traveling downhill at aconstant velocity, the power from the drive wheels may be coupled backto the motor-generator 54 for generating electrical energy, thusreducing an amount of conventional frictional braking required tooperate the vehicle. When the field coils of the motor-generator 54 areenergized, the motor acts as an electrical energy generator forconverting power on the first shaft 58 to electrical power for chargingthe storage element 16. The torque required at the first shaft 58 togenerate the electrical energy acts as a braking force on the drivewheels 24.

In other embodiments where the motor-generator 54 comprises, forexample, a permanent magnet field DC motor, operation as a generator iscontingent on whether or not current is drawn from the motor while themotor is receiving mechanical power. In such cases the power converter55 may be configured to enable or disable drawing of a charging currentto charge the storage element 16 depending on whether braking isrequired.

In general, in the hybrid vehicle embodiments shown in FIG. 1 and FIG.2, the required operating power may be apportioned between the motor andthe engine respectively, such that the motor supplies the first portionof the operating power and the engine supplies the second portion of theoperating power. Advantageously the apportionment of power between themotor and the engine facilitates operation of the hybrid vehicles 11 and50 such that a cost of operating the vehicles may be minimized.

In accordance with one embodiment of the invention, minimizing theoperating cost involves producing operating costs for a plurality ofapportionments of a requested operating power between the engine 52 andthe motor-generator 54 and selecting an apportionment from the pluralityof apportionments corresponding to a minimum operating cost. Theprocessor circuit 80 then produces the engine power control signal atthe output 96 and motor power control signal at the output 98 inaccordance with the selected apportionment.

The selected apportionment of power is applied for a control period,after which the process is repeated for successive control periods, thusresponding to operating changes on an ongoing basis. When theapportionment of power results in no power being supplied by the engine52, the processor circuit 80 may cause the clutch control signal toassume the disengaged state causing the clutch 64 to be disengaged, thusallowing the engine to be stopped such that fuel is conserved. Whenrequired the engine 52 may be restarted by engaging the clutch 64 tocouple power to the third shaft 62, thus starting the engine.

Engine Operating Costs

Still referring to FIG. 2, the cost of operating the engine 52 to supplya quantity of operating power to the vehicle is related to an amount offuel consumed from the fuel reservoir 30. The engine 52 may beconfigured to run on one or more of a variety of fuel supplies,including but not limited to, gasoline, diesel, biogas or otherbio-fuels including cellulosic and other ethanols, propane, etc.

Referring to FIG. 4, a graphical depiction of a fuel consumption map forthe engine 52 is shown generally at 160. The map 160 includes a surfacefunction 162 which relates engine speed values 164 and engine torquevalues 166 to fuel consumption values 168. Each pairing of a specificengine speed value 164 and an engine torque value 166 represents a powersupplied by the engine 52 (Power=Torque×speed). In general, datarepresenting the map 160 is stored in the store 136 in the parametermemory 124 of the processor circuit 80. The data may be stored as a lookup table or a set of coefficients for a function defining the surface162.

In the embodiment shown in FIG. 2, the fuel consumption data stored inthe store 136 is updated with actual fuel consumption values produced bythe fuel consumption sensor 92 and received at the input 94 of the I/O128. In other embodiments, where a fuel consumption sensor is notincluded, the fuel consumption data stored in the store 136 may bedetermined from test data for the engine 52, or from standard test datafor engines similar to the engine 52.

Fuel consumption is also generally dependent on engine temperature. Inthe embodiment shown, the effect of engine temperature on fuelconsumption is taken into account by storing a cold engine temperaturefuel consumption map and a hot engine temperature fuel consumption mapin the store 136 of the parameter memory 124. The temperature signalfrom the temperature sensor 88 is received at the input 90 of the I/O128 and the actual engine temperature is used to interpolate between thehot and cold fuel consumption values to obtain a temperature correctedfuel consumption value.

In this embodiment, the engine operating cost is calculated from thefollowing equation:OC_(eng)=Fuel_(eng)·Power_(eng)   Eqn 1where OC_(eng) is the operating cost of the engine, Power_(eng) is anapportionment of power to be supplied by the engine 52 and Fuel_(eng) isthe fuel consumption value corresponding to the apportionment of power.Motor Operating Costs

Electrical energy for operating the motor-generator 54 is supplied fromthe storage element 16. In general, the cost of operating themotor-generator 54 may be related to the cost of replacing energysupplied from the storage element 16. Electrical energy supplied fromthe storage element 16 may be replaced by coupling regenerative brakingpower from the drive wheels 24 to the motor-generator 54, or by couplingmechanical power supplied by the engine 52 to the motor-generator 54, togenerate electrical energy for charging the storage element.

In this embodiment the motor operating cost is calculated from thefollowing equation:OC_(mot)=Fuel_(equ)·Power_(mot)   Eqn 2where OC_(mot) is the operating cost of the motor, Power_(mot) is theapportionment of power to be supplied by the motor and Fuel_(equ) is anequivalent fuel consumption amount that will be required by the engine52 to replace the quantity of energy in the storage element 16 in afuture control period.

In this embodiment Fuel_(equ) is calculated taking into account thelowest fuel consumption rate (from the map shown in FIG. 4) and theelectrical losses (or efficiencies) in the storage element 16 and themotor-generator 54 as follows:

$\begin{matrix}{{Fuel}_{equ} = \frac{{{Min}( {Fuel}_{eng} )} - {Fuel}_{free\_ brake}}{\eta_{mot} \cdot \eta_{store}}} & {{Eqn}\mspace{14mu} 3}\end{matrix}$where Fuel_(free) _(_) _(brake) is an amount of energy received fromregenerative braking of the vehicle 50 during a prior control period,expressed as an equivalent fuel consumption, η_(mot) is the electricalefficiency of the motor-generator 54, and η_(store) is the chargingefficiency of the storage element.

In general, the quantity of the energy available from regenerativebraking will vary in accordance with driving habits of the vehicleoperator, road and environmental conditions etc. Accordingly, in thisembodiment the quantity of energy is calculated in real time using thefollowing equation:

$\begin{matrix}{E_{free\_ brake} = {\frac{1}{T}{\int_{0}^{T}{{Power}_{free\_ brake}\mspace{11mu}{\mathbb{d}t}}}}} & {{Eqn}\mspace{14mu} 4}\end{matrix}$where T is a control loop repetition time and Power_(free) _(_) _(brake)is the instantaneous regenerative braking power available at any time t.The regenerative braking energy calculated in Eqn 4 is available for useduring the next control period. The quantity E_(free) _(_) _(brake) maybe converted into an equivalent fuel consumption Fuel_(free) _(_)_(brake) using standard values for the potential energy per unit massfor the fuel type contained in the fuel reservoir 30.

In general, the fuel consumption of the engine 52 thus includes a firstcomponent related to supplying a portion of operating power to the drivewheels 24 from the engine, and a second component, which is attributedto the motor-generator 54, for supplying power to the motor in order tocharge the storage element 16 to replace energy discharged therefrom ina previous control period.

Storage Element Lifetime Cost

Commonly available storage elements have an associated lifetime, afterwhich the element becomes unsuitable for further use. For some storageelements, such as NiMH batteries, this lifetime may be prolonged byoperating the element as close as possible to an optimal state of charge(SOC), for example at 60% of full capacity. Advantageously, operatingthe storage element 16 at close to optimal SOC results in a longerlifetime and thus the lowest storage element lifetime cost.

Referring to FIG. 5 a graphical depiction of an exemplary NiMH storageelement lifetime as a function of SOC is shown generally at 180. In thisexample, the longest lifetime is achieved by maintaining the battery SOCat 60%. Any deviation from 60% SOC results in a storage element lifetimepenalty or reduction. In practice, it is difficult to maintain a storageelement at or very near the optimal SOC at all times, and the storageelement is generally operated over a range of SOC values, for examplefrom 40% SOC to 80% SOC for a NiMH storage element.

Whenever electrical energy is supplied from the storage element(discharging), or supplied to the storage element (charging), theresulting SOC of the storage element will change. In any control period,if the electrical energy supplied results in the SOC moving away fromthe optimal SOC there is an associated lifetime penalty or operatingcost which in this embodiment is expressed as:OC_(storage) =W _(s) ·|K·ΔSOC−Power_(mot)|   Eqn 5where K is a calibration parameter for relating an SOC difference to apower required to bring the SOC to the storage element 16 back tooptimal SOC, and W_(s) is a weighting factor. The weighting factor W_(s)may be used to account for the relative cost of fuel versus the relativecost of storage element replacement. For example, if fuel prices dropthe weighting factor W_(s) may be increased to accord greater weight tothe storage element operating costs, while if storage elementreplacement prices drop, the weighting W_(s) may be reduced to accordless weight to the storage element operating costs.

For example, referring to FIG. 5, if at the beginning of the controlperiod the SOC is at a point 182 (corresponding to a SOC ofapproximately 70%), then the ΔSOC (shown by the arrow 184) is −10%.Assuming that K=1000 W per % SOC, the required power to return tooptimal SOC is −10000 W (the negative sign indicates a discharge of thestorage element 16 is required). For a motor power apportionment of10000 W, the operating cost calculated from Eqn 5 is thus zero, sincedischarging 10000 W from the storage element causes the SOC to be atoptimal SOC. Lower or higher motor power apportionments will result inpositive storage element operating costs since the SOC will not be atoptimal SOC at the end of the control period.

Overall Operating Cost

The overall operating cost function is obtained by summing the engineoperating cost, the motor operating cost and the storage elementoperating cost i.e:OC=OC_(eng)+OC_(mot)+OC_(storage)   Eqn 6where OC is the overall operating cost. In general the overall operatingcost function is evaluated for each of a plurality of apportionments ofpower between the engine 52 and the motor-generator 54 and the powerapportionment corresponding to a minimum operating cost is selected. Theplurality of apportionments are identified by evaluating operationalconstraints associated with the engine 52, the motor-generator 54, andthe storage element 16 prior to each control period, such that powerapportionments that do not meet the constraints are not considered. Someof the constraints may be set by the manufacturer (e.g. maximum storageelement temperature, maxim terminal voltage, and/or minimum terminalvoltage), however in general the constraints also depend on the currentoperating conditions of the vehicle.

The engine 52 has a constraint related to the maximum power that may besupplied, which is a function of the engine speed and torque.Accordingly, an apportionment which results in an engine torque or speedthat is greater than the corresponding maximum is not furtherconsidered.

The motor-generator 54 also has a constraint related to the maximummechanical power that may be supplied which may be expressed as afunction of motor temperature, motor current, motor voltage, motor speedand motor torque. When regenerative braking power is available, themotor-generator 54 has a further constraint related to the maximummechanical power that may be received by the motor, which is a functionof motor temperature, motor current, motor voltage, motor speed andmotor torque.

Another constraint for the motor-generator 54 occurs when a powerapportionment to the motor will result in overcharging of the storageelement (i.e. the resulting SOC at the end of the control period wouldbe above the maximum SOC recommended by the storage elementmanufacturer). Similarly, a constraint for the motor-generator 54 occurswhen a motor power apportionment will result in discharging the storageelement 16 beyond a minimum SOC set by the manufacturer.

Any motor power apportionment that exceeds any of the motor constraintsis not further considered.

The storage element 16 generally has constraints related to maximumcharging power and maximum discharging power. For example, the maximumcharging power constraint for an NiMH battery is a function of batterytemperature, SOC, the terminal voltage of the battery, maximum terminalvoltage, and maximum charging current. In general the maximum changingpower varies from control period to control period depending on theaforementioned factors.

Similarly, the maximum discharging power for a NiMH battery is afunction of battery temperature, SOC, the terminal voltage of thebattery, minimum terminal voltage, and maximum discharging current.

Accordingly, an apportionment which exceeds any of the storage elementcharging or discharging constraints is not further considered.

Control Loop

Referring to FIG. 6, a flow chart depicting blocks of code for directingthe processor circuit 80 (shown in FIG. 2) to manage power in the hybridvehicle 50, is shown generally at 200. The blocks generally representcodes that may be read from the computer readable medium 130, and storedin the program memory 122, for directing the CPU 120 to perform variousfunctions related to managing apportionment of power in the vehicle 50.The actual code to implement each block may be written in any suitableprogram language, such as C, C++ and/or assembly code, for example.

The process begins with a first block of codes 202 which directs theprocessor circuit 80 to receive the drive signal from the operator inputdevice at the input 82 and to receive the speed from the speed sensor 72at the input 84 of the I/O 128.

The process continues at block 204, which directs the CPU 120 to read acurrent set of operating conditions of the hybrid vehicle 50 from thestore 138 in the parameter memory 124. The current operating conditionsgenerally include, for example, conditions such as speed and torque ofthe engine 52 and the motor-generator 54, SOC & terminal voltage of thestorage element 16, temperatures of the engine, motor, power converter55, and storage element, etc. The block 204 may also include codes fordirecting the processor to calculate a current vehicle acceleration fromthe speed values.

Block 204 further directs the processor circuit 80 to calculate anamount of operating power to be supplied to drive the vehicle 50 for thenext control loop period. The amount of operating power to be suppliedis calculated in response to the drive signal received from the operatorinput device 70 and the current operating conditions of the vehicle.Accordingly, the amount of operating power to be supplied may not meetthe operator requested power, depending on current operating conditionsof the vehicle 50. For example, if the engine 52 and motor-generator 54are already delivering maximum power, a request received from theoperator input device 70 to supply more power will not be met.

The process continues at block 206 which directs the processor circuit80 to evaluate operating constraints for the next control loop periodfor the engine 52, motor-generator 54, and storage element 16. Theconstraints are evaluated based on operating conditions read at block204. Block 206 may further direct the processor circuit 80 to readconstraint limits from the store 140 in the parameter memory 124, whichmay include manufacturer and/or other constraint information for theengine 52, the motor-generator 54 and/or the storage element 16.

The process continues at block 208 which directs the processor circuit80 to read control loop parameters from the store 142 in the parametermemory 124. The control loop parameters may include, for example, apower increment value which determines the number of differentapportionments of power that will be evaluated. Evaluating a greaternumber of apportionments may provide more precise apportionments, butsince the operating costs are evaluated in real time while operating thevehicle, evaluating a large number of apportionments may requireprovision of faster processing speed for the processor circuit 80. Block208 further directs the processor circuit to initialize a powerapportionment variable to a first power apportionment.

Block 210 then directs the processor circuit to calculate the operatingcosts for the engine 52, motor-generator 54, and storage element 16 forthe first power apportionment.

At block 212, if the present power apportionment is not the last powerapportionment, the process continues at block 214, where the powerapportionment variable is set to the next power apportionment. Blocks210, 212 and 214 are then repeated for successive power apportionments.

Referring to FIG. 7, a graphical depiction of the operating costs forapportionment of a required power of 50 kW is shown generally at 200.Power apportionments are plotted on the x-axis as pairs of powerapportionments 242, each pair including an engine power apportionment244 and a motor power apportionment 246. A curve 248 represents theengine operating cost calculated in accordance with Eqn 1 for the powerapportionments, a curve 250 represents motor operating costs calculatedin accordance with Eqn 2, and *a curve 252 represents storage elementlifetime costs calculated in accordance with Eqn 5. A curve 254represents the overall operating cost function calculated in accordancewith Eqn 6, for each power apportionment 242. In the example shown inFIG. 7, for simplicity it is assumed that no regenerative braking energyis available for the control period in question.

Referring back to FIG. 6, if at block 212 the power apportionment is thelast power apportionment then the process continues at block 216.

At block 216 the processor circuit is directed to execute anoptimization search to find an apportionment 242 corresponding to theminimum operating cost in the curve 254. In this embodiment, a goldensection search is used to find the minimum operating cost. The goldensection search is a bracketing technique, which may be applied to a setof values to find a single minimum value in the set between an upperbound bracket value and a lower bound bracket value. The search beginsby selecting upper and lower bound brackets at end points of the rangeof power apportionments 242. The upper and lower bound brackets are thensuccessively narrowed until a minimum is found. The technique derivesits name from the golden ratio, which has been found to be an effectivebracketing ratio. Applying the golden ratio involves selecting anintermediate apportionment between the upper bound bracket and the lowerbound bracket that is 0.38197 from one end and 0.61803 from the otherend, and then moving the bracket having a greater correspondingoperating cost (curve 254) to the intermediate apportionment, which thenbecomes the new upper or lower bound bracket. The process is thenrepeated until the minimum operating cost value coincides with eitherthe upper bound bracket or the lower bound bracket, in which case thelesser of the cost values corresponding to the upper and lower boundbrackets is the minimum operating cost value.

The application of the golden section search technique to finding theminimum operating cost is described with reference to FIG. 7, byassuming that the number of apportionments is six (i.e theapportionments [0,50], [10,40], [20,30], [30,20], [40,10], and [50,0]).The first step in the application of the technique is to selectapportionment pair [0,50] as the lower bound bracket and [50,0] as theupper bound bracket, and to calculate an intermediate point 256 betweenthe upper bound bracket and the lower bound bracket using the goldensection ratio of 0.38197, yielding an intermediate apportionment of[20,30], which is closest to the ratio 0.38197. Since the operating costvalue at [20,30] is approximately 0.082, which is smaller than theoperating cost values at [0,50] and [50,0], a new lower bound bracket of[20,30] is selected. Using the new lower bound bracket of [20,30] andthe upper bound bracket of [50,0], the golden ratio is again applied tofind an intermediate point 258, which in this case is closest to theapportionment [30,20] with an operating cost value of approximately0.066. The lower bound bracket [20,30] has a higher cost value andaccordingly, the new lower bound bracket is chosen at [30,20]. Selectinga further intermediate point in accordance with the golden ratio yieldsan intermediate point 260, which is close to apportionment [40,10].Because there are no further intermediate values between the [40,10]lower bracket value and the [50,0] upper bound bracket value, theminimum of these two values represents the minimum operating cost at262, which in this case is approximately 0.061 and corresponds to anapportionment of [40,10].

Advantageously, when the number of possible power apportionments islarge, the golden section search allows quick convergence on a minimumvalue in a plurality of values having a single minimum between an upperbound and a lower bound. In other embodiments alternative optimizationtechniques, such as a linear search, for example may be used to find theminimum operating cost.

Referring back to FIG. 6, the process continues at block 218, whichdirects the processor circuit to cause the engine power control signaland the motor power control signal to be generated at respective outputs96 and 98 of the I/O 128. In this case the engine supplies 40 kW ofpower and the motor supplies 10 kW, and thus the processor circuit 80also causes the clutch control signal to be produced at the output 104to cause the clutch 64 to be engaged such that the engine is coupled tothe second shaft 60.

Advantageously, including a storage element lifetime cost and fuelconsumption costs in selecting the apportionment of power between theengine and the motor facilitates operation of the vehicle such that fuelconsumption is reduced without reducing the lifetime of the battery.

Referring to FIG. 8, an alternative embodiment of a hybrid vehicle isshown generally at 280. The hybrid vehicle 280 includes an engine 282, atransmission 284, a motor 286, and a storage element 288. The engine 282is coupled to the drive wheels 24 through the transmission 284. In thisembodiment the transmission includes a take-off point 290 for couplingto the motor 286. The motor 286 is coupled to a storage element 288 forsupplying and receiving electrical energy as described above. The takeoff point 290 and motor 286 are configured in a manner similar to astarter motor in a conventional internal combustion engine vehicle,although the motor 286 is generally larger than a conventional startermotor and has a higher power capability. One example of this embodimentis a so-called “mild hybrid” in which the engine 282 shuts down when thevehicle is stopped, and the motor 286 restarts the engine when theoperator produces a drive signal at an operator input device 192, thusconserving fuel when stopped. In the embodiment shown in FIG. 8, theprocessor circuit 80 shown in FIG. 2 may be implemented generally asdescribed above to manage power in the hybrid vehicle 280.

While specific embodiments of the invention have been described andillustrated, such embodiments should be considered illustrative of theinvention only and not as limiting the invention as construed inaccordance with the accompanying claims.

What is claimed is:
 1. A method for managing power in the hybridvehicle, comprising: determining, based at least in part on one or moreoperating conditions of the hybrid vehicle, an amount of operating powerto be supplied in response to a drive signal generated based on operatorinput; determining, for each of a plurality of apportionments of theoperating power between an engine of the hybrid vehicle and amotor-generator of the hybrid vehicle, an overall operating cost value,each overall operating cost value accounting for at least a cost valueassociated with the engine of the hybrid vehicle and one or moreconstraints of a storage element of the hybrid vehicle; selecting anapportionment of the operating power from among the plurality ofapportionments of the operating power, the selected apportionment beingthe apportionment with a minimum determined overall operating costvalue; and causing the operating power to be supplied by at least one ofthe engine and the motor-generator in accordance with the selectedapportionment.
 2. The method of claim 1, wherein the cost valueassociated with the engine of the hybrid vehicle comprises an enginefuel consumption cost determined based at least in part on a fuel price.3. The method of claim 1, further comprising receiving a signalrepresenting an operating temperature of the engine, the cost valueassociated with the engine of the hybrid vehicle corresponding to theoperating temperature of the engine.
 4. The method of claim 1, wherein:the cost value associated with the engine of the hybrid vehiclecomprises an engine fuel consumption cost; and for a particularapportionment of the operating power among the plurality ofapportionments of the operating power, the engine fuel consumption costis determined based at least in part on a fuel consumption costassociated with operating the engine to supply the particularapportionment of power.
 5. The method of claim 1, wherein the one ormore constraints of the storage element of the hybrid vehicle accountfor the state of charge of the storage element.
 6. The method of claim1, wherein the one or more constraints of the storage element of thehybrid vehicle account for the temperature of the storage element. 7.The method of claim 1, wherein the one or more constraints of thestorage element of the hybrid vehicle account for the voltage present onthe storage element.
 8. An apparatus for managing power in a hybridvehicle, the vehicle comprising an engine, an electric motor, and astorage element coupled to the electric motor, the apparatus comprisinga controller operably configured to: determine, based at least in parton one or more operating conditions of the hybrid vehicle, an amount ofoperating power to be supplied in response to a drive signal generatedbased on operator input; determine, for each of a plurality ofapportionments of the operating power between the engine of the hybridvehicle and the electric motor of the hybrid vehicle, an overalloperating cost value, each overall operating cost value accounting forat least a cost value associated with the engine of the hybrid vehicleand one or more constraints of the storage element of the hybridvehicle; select an apportionment of the operating power from among theplurality of apportionments of the operating power, the selectedapportionment being the apportionment with a minimum determined overalloperating cost value; and cause the operating power to be supplied by atleast one of the engine and the motor-generator in accordance with theselected apportionment.
 9. The apparatus of claim 8, wherein the costvalue associated with the engine of the hybrid vehicle comprises anengine fuel consumption cost determined based at least in part on a fuelprice.
 10. The apparatus of claim 8, wherein the controller is furtheroperably configured to receive a signal representing an operatingtemperature of the engine, wherein the cost value associated with theengine of the hybrid vehicle corresponds to the operating temperature ofthe engine.
 11. The apparatus of claim 8, wherein: the cost valueassociated with the engine of the hybrid vehicle comprises an enginefuel consumption cost; and for a particular apportionment of theoperating power among the plurality of apportionments of the operatingpower, the engine fuel consumption cost is determined based at least inpart on a fuel consumption cost associated with operating the engine tosupply the particular apportionment of power.
 12. The apparatus of claim8, wherein the one or more constraints of the storage element of thehybrid vehicle account for the state of charge of the storage element.13. The apparatus of claim 8, wherein the one or more constraints of thestorage element of the hybrid vehicle account for the temperature of thestorage element.
 14. The method of claim 8, wherein the one or moreconstraints of the storage element of the hybrid vehicle account for thevoltage present on the storage element.
 15. A hybrid vehicle comprising:an engine; an electric motor; an energy storage element coupled to themotor; and a controller, the controller operably configured to:determine, based at least in part on one or more operating conditions ofthe hybrid vehicle, an amount of operating power to be supplied inresponse to a drive signal generated based on operator input; determine,for each of a plurality of apportionments of the operating power betweenthe engine of the hybrid vehicle and the electric motor of the hybridvehicle, an overall operating cost value, each overall operating costvalue accounting for at least a cost value associated with the engine ofthe hybrid vehicle and one or more constraints of the storage element ofthe hybrid vehicle; select an apportionment of the operating power fromamong the plurality of apportionments of the operating power, theselected apportionment being the apportionment with a minimum determinedoverall operating cost value; and cause the operating power to besupplied by at least one of the engine and the motor-generator inaccordance with the selected apportionment.
 16. The hybrid vehicle ofclaim 15, wherein the cost value associated with the engine of thehybrid vehicle comprises an engine fuel consumption cost determinedbased at least in part on a fuel price.
 17. The hybrid vehicle of claim15, wherein the controller is further operably configured to receive asignal representing an operating temperature of the engine, wherein thecost value associated with the engine of the hybrid vehicle correspondsto the operating temperature of the engine.
 18. The hybrid vehicle ofclaim 15, wherein: the cost value associated with the engine of thehybrid vehicle comprises an engine fuel consumption cost; and for aparticular apportionment of the operating power among the plurality ofapportionments of the operating power, the engine fuel consumption costis determined based at least in part on a fuel consumption costassociated with operating the engine to supply the particularapportionment of power.
 19. The hybrid vehicle of claim 15, wherein theone or more constraints of the storage element of the hybrid vehicleaccount for the state of charge of the storage element.
 20. The hybridvehicle of claim 15, wherein the one or more constraints of the storageelement of the hybrid vehicle account for the temperature of the storageelement.
 21. The method of claim 15, wherein the one or more constraintsof the storage element of the hybrid vehicle account for the voltagepresent on the storage element.